1. Field of the Invention
The present invention relates to an inductor and more particularly, to a surface mount inductor constructed for use in high-frequency circuits and other electronic apparatuses.
2. Description of the Related Art
A conventional surface mount inductor is shown in FIGS. 11 and 12. FIG. 11 is a perspective view showing the appearance of the inductor 1 and FIG. 12 is a development view of an electrode. In the inductor 1, terminal electrodes 3 and 4 are provided at both ends of a columnar winding core material which has a spiral coil 2 provided on an external surface thereof. The spiral coil 2 is arranged such that after a thin-film conductor has been formed on the entire surface of the columnar winding core material, a spiral groove 5 is formed in the thin-film conductor. The terminal electrodes 3 and 4 are ring-shaped so as to extend around the columnar winding core.
When an electric current flows through the inductor 1, electric current I flows into the initial end portion 2a of the spiral coil 2 via the terminal electrode 3 as shown in FIG. 12. Then, the electric current I, which has flowed through the spiral coil 2, flows from the inductor 1 from the end 2b via the terminal electrode 4.
Since the terminal electrodes 3 and 4 extend around the winding core, the electrodes function as a coil with one turn, that is, as a short-circuited ring. Accordingly, the magnetic field generated by the electric current flowing through the spiral coil 2 crosses the terminal electrodes 3 and 4 which are parallel to the spiral coil 2, and an induced current i flows through the terminal electrodes 3 and 4, respectively. In FIG. 12, the induced current i flowing through the terminal electrode 4 is not shown. The induced current i dissipates energy while it circulates through the terminal electrodes 3 and 4. Therefore, the conventional inductor 1 has a problem in that the Q-factor and inductance of the spiral coil 2 are very low.
Up to now, as a solution to this problem, a method of separating the spiral coil 2 and the terminal electrodes 3 and 4 and electrically connecting the coil 2 and electrodes 3 through a lead-out pattern was used. However, this method requires that the inductors be large and prevents the required reduction in weight and size reduction. Thus, it is not possible to use the lead-out pattern.
In order to overcome the problems described above, preferred embodiments of the present invention provide a small inductor having substantially circular electrodes that are prevented from functioning as a short-circuited ring, while achieving a very high Q-factor and inductance.
According to one preferred embodiment of the present invention, an inductor preferably includes a winding core, a coil conductor extending spirally around the winding core, substantially circular electrodes running nearly around the winding core and located outwardly of the coil conductor, and dividing grooves extending from the ends of the coil conductor over the substantially circular electrodes. Here, the length of the dividing groove is, for example, a half or more of the diameter of the coil conductor.
Since the substantially circular electrodes are partially divided by the dividing grooves, the substantially circular electrodes are prevented from functioning as a short-circuited ring. That is, even when the magnetic flux generated by the current flowing through the coil conductor crosses the substantially circular electrodes, it is difficult for the circulating currents to flow through the substantially circular electrodes.
Therefore, an inductor having superior characteristics can be obtained in which energy loss is suppressed and decreases in the Q-factor and the inductance of the coil conductor are prevented.